London: British Prime Minister David Cameron said Friday he would join in the mass rally being staged in Paris in the wake of the massacre at French satirical magazine Charlie Hebdo.
"I`ve accepted President Hollande`s invitation to join the Unity Rally in Paris this Sunday -- celebrating the values behind Charlie Hebdo", he said on his personal Twitter account.
The "Republican march" is expected to draw hundreds of thousands of people onto the Paris streets in a show of French national unity, upholding the principles of the state.
The British flag was flown at half-mast over Cameron`s Downing Street office on Thursday.
Cameron said in the aftermath of the Charlie Hebdo attack that Western allies should defend their values of democracy and freedom of expression.
In a statement on Wednesday, he said: "What has happened in Paris is an appalling terrorist outrage and I know that everyone in Britain will want to stand with the French government and with the French people at this time.
"We must never allow the values that we hold dear, of democracy, of freedom of speech to be damaged by these terrorists.
"We must stand against what they have done and I feel huge sympathy for everyone in France, particularly for the families of those who have lost loved ones."
Britain`s official terror threat was raised to "severe" in August -- the second-highest of five levels -- meaning that an attack is considered "highly likely".
Andrew Parker, head of Britain`s MI5 domestic intelligence agency, said Thursday that Islamist militants in Syria were planning "mass casualty attacks" on Western targets, saying the attacks in Paris were only a reminder of an ongoing threat.